This invention relates to a method and apparatus for automatically tracking a magnetic tape.
Where, with a magnetic recording-reproduction apparatus using a magnetic tape, for example, a fixed magnetic head type recording-reproduction apparatus, the magnetic tape happens to move vertically during its run, the tracks of the magnetic tape are displaced from the magnetic head gaps (hereinafter referred to as "a track displacement"). This event is known to change the waveform level of a reproduction signal. Variation in the waveform of a reproduction signal gives rise to flickers of fluctuating brightness and consequently resulting in the deterioration of a picture quality. On the other hand, a high density recording is demanded to save the consumption of a magnetic tape. The conventional process of meeting this requirement comprises reducing not only a video track but also a track pitch. However, an attempt to contract the video track has the drawback of causing the track displacement to readily appear in case of the vertical shifting of the running magnetic tape, with a noticeable change in the waveform level of a reproduction signal.
It has hitherto been tried to suppress the occurrence of the track displacement by providing, for example, a guide post fitted with a pair of flanges for a tape-forwarding mechanism. Such prior art process is intended to prevent a magnetic tape from being vertically shifted by causing the upper and lower edges of the magnetic tape to contact the paired flanges of the guide post. As a result, a mechanical stress is applied to the upper and lower edges of the magnetic tape with the resultant frequent damage thereof.